Process for producing a formable collagen dispersion

ABSTRACT

AN AIR-FREE COLLAGEN SLURRY CAN BE MIXED WITH AN AIRFREE SWELLING AGENT AND THE MIXTURE CAN THEN BE SUBJECTED TO SHEARING ACTION TO OBTAIN A UNIFORMLY SWOLLEN COLLAGEN DISPERSION FROM WHICH COLLAGEN STRUCTURES CAN BE SUBSEQUENTLY FABRICATED.

Aug. 15, 1972 J. J. GRABAUSKAS PROCESS FOR PRODUCING A FORMABLE COLLAGENDISPERSION Original Filed Oct. .11, 1967 2 Sheets-Sheet 1 INVENTORJOSEPH J. GRABAUSKAS 7 +L 4--4-v- ATTORNEY 15,1972 J. J. GRABAUSKAS3,684,732

PROCESS FOR PRODUCING A FORMABLE COLLAGEN DISPERSION Original Filed Oct..11, 1967 2 Sheets-Sheet 2 INVENTOR F JOSEPL-i GRABA/(USKAS L 'gfg /wwATTORNEY United States Patent 3,684,732 PROQESS FOR PRODUCING A FORMABLECOLLAGEN DISPERSION Joseph J. Grabauskas, Chicago, Ill., assignor toUnion Carbide Corporation Original application Oct. 11, 1967, Ser. No.674,575. Divided and this application Apr. 29, 1969, Ser. No.

Int. Cl. B011 13/00 US. Cl. 252-311 8 Claims ABSTRACT OF THE DISCLOSUREAn air-free collagen slurry can be mixed with an airfree swelling agentand the mixture can then be subjected to shearing action to obtain auniformly swollen collagen dispersion from which collagen structures canbe subsequently fabricated.

This application is a division of application Ser. No. 674,575, filedOct. 11, 1967, now abandoned.

This invention relates to the mixing of a plurality of materials. Moreparticularly, this invention relates to the homogeneous mixing ofcollagen with a liquid swelling agent to obtain a high solidsconcentration mass of uniformly swollen collagen.

The production of homogeneous mixtures is replete with problems. Forexample, in the preparation of collagen-liquid blends in which theamount of liquid present in the blend is less than that which thecollagen is capable of imbibing, uniform distribution of the liquid withthe collagen mass and, consequently, uniform swelling of the collagenis, at best, extremely difficult to attain. Generally, there is atendency for the first portions of the collagen contacted by the liquidto rapidly imbibe to their capacity thus consuming the liquid beforeother portions of the collagen can be brought into contact with theliquid. The resultant collagen-liquid blend is characterized by aportion of the collagen containing essentially all of the swelling agentand another portion in which the collagen is in the form of lumps ofunswollen collagen which are usually matted together and encapsulated bythe viscous, swollen collagen. Subsequent homogenization of the blend isextremely difficult due to the high viscosity of the blend and thesusceptibility of the collagen to be degraded by the local frictionalheat produced by the high shear forces which are concomitant withmixing.

When collagen is extruded in the form of tubing, films, sheets, fibers,and the like, a high collagen concentration in the blends is desirablein order to provide rapid coagulation and/or drying. Processing of highsolids concentration compositions by the methods presently in usegenerally require extensive mechanical processing, usually involve arecirculating system, and can result in degradation or denaturation tosuch an extent that the resultant products are not satisfactory. Use oflow shear rates generally avoid the problem of local overheating andconsequent degradation of the collagen in a highly viscous mass but tendto interfere with attaining homogeneity of and freedom from lumps in theblend which are desired for continuous extrusion of thin casings. Inaddition, the viscous, high-solids collagen blends are difficult toprocess without air entrapment. Entrapped air causes structuralweaknesses and imperfections in the formed structures while the presenceof lumps can interrupt the desired continuity of the desired article inthe extrusion operation.

It is an object of the present invention, therefore, to provide a methodand apparatus by which collagen can be Ice homogeneously mixed with aswelling agent and obtain therefrom a uniformly swollen collagen blendhaving a high concentration of solids.

This and further objects of the present invention will become moreapparent from the ensuing description.

It has now been found that the objects of this invention can begenerally attained by delivering a relatively low viscosity,substantially air-free collagen suspension to a first zone; delivering alow viscosity, air-free swelling,

agent to a second zone; mixing said swelling agent and collagen in amixing zone and immediately subjecting the mixed mass to a shearingaction, continuing the shearing action while the mass is moved throughthe mixing zone and the collagen particles in the suspension becomeswollen; maintaining the swelling agent-collagen mixture in the form ofa thin, sheet-like mass throughout the length of said mixing zone whilemaintaining the mixture in said mixing zone at a predeterminedtemperature; and

extruding said mixture in the form of an endless, selfsupportingstructure.

To practice the present invention, a mixing apparatus, hereinafterreferred to as a homogenizer, can be employed which comprises, incombination, a housing, a rotor within said housing, a plurality ofspaced inlets at one end of said housing and an outlet from said housingspaced from said inlets, said rotor having a plurality of smallprotuberances along a major portion of its length, the distance betweenthe planar surface defined by said protuberances and the inside wall ofsaid housing being such that a flow path is provided from each inlet tothe end of and along the major portion of the length of said rotor.

The collagen suplied to the homogenizer can be prepared by any knownmethod such as cleaning a collagencontaining tissue, as for example,tendon or fresh or limed animal hide, and then comminuting the collagento the desired size.

The preliminary comminuting is preferably performed at a low temperaturethrough the use of a coolant such as ice, and can be carried out by theuse of any well known means such as in a conventional meat grinder.

The comminuted collagen can then be mixed with a liquid coolant such aswater. The collagen does not imbibe the liquid to such an extent as toform a viscous blend unless a swelling agent is present. Thus, thecollagen can be diluted with water to yield, for example, a 10 percentdry solids mixture which would be characterizable as a solid in liquidsuspension rather than an extrudable or formable viscous composition.The terms extrudable or formable composition as used throughout thisapplication and in the appended claims should be understood as and areintended to refer to the ability to process a mixture in conventionalequipment, such as an extruder, and obtain therefrom a formed structure.

The collagen-liquid mixture is then subjected to a fibrillationoperation by use of, for example, an apparatus normally used to preparemeat emulsions. The term fibrillation as employed herein refers to theact of subdividing the collagen into a suspension of fibrous particlesin order to prepare it for swelling, the fibrous suspension containingsufficient liquid such that the solids content of the fibrous collagensuspension can be from about 3%15% by weight or higher of the totalcomposition.

The invention will become more clear when taken together with theaccompanying drawing which is set forth as being exemplary andillustrative of the apparatus that can be employed as is not intended,in any way, to be limitative thereof and wherein:

FIG. 1 is a diagrammatic illustration of one embodiment by which theinvention can be practiced;

FIG. 2 is a side elevation view, part in section, of one embodiment ofthe homogenizer apparatus of the invention; and

FIG. 3 is an exaggerated view of the apparatus of FIG. 2 taken throughline 33 thereof.

Turning now to the drawing, wherein like reference numerals denote likeparts, there is shown in H6. 1 one manner by which the preparedcollagen, which is basically in the form of a slurry 10, is fed to apressurized vessel 12, which can be cooled by any convenient means, suchas an ice water bath 14.

The pressurized vessel 12 can be maintained under a pressure of fromabout 30 to 80 pounds per square inch (p.s.i.) through the use ofcompressed air, nitrogen or the like, which is supplied to an upperportion of the pressurized vessel 12.

A stirrer 16, can be employed in the pressurized vessel 12 to preventany solids from settling out and to provide for the proper distributionof collagen. A conventional metering pump 18 delivers the collaganslurry 10, under pressure, through conduit 19 and inlet port 26 to ahomogenizer, generally indicated by reference numeral 20.

For the preparation of formable collagen compositions having desired orrequired concentrations for use in producing sausage casing or otherextrudable or formable structures, the collagen must be mixed with aswelling agent. Suitable swelling agents are those materials which willcause collagen to imbibe appreciable amounts of fluids over and abovethe normal moisture content of collagen when in contact with water.

Any of the known swelling agents such as dilute acids or dilute alkalisand salts can be used. Preferred for use as swelling agents are dilutesolutions of hydrochloric, lactic and acetic acids and dilute solutionsof sodium hydroxide.

A swelling agent solution 22 can be delivered, under pressure, from asuitable supply reservoir 23 to the homogenizer 20 through inlet port 28by means of a second conventional metering pump 24 and conduit 25.

The flow rates of the swelling agent 22 and the collagen slurry aremetered by the pumps 24 and 18, respectively, and are maintained at aratio so that, after mixing and swelling in the homogenizer 20, thecollagen-swelling agent blend can be transferred therefrom throughdischarge outlet 40 to obtain an extrudable or formable composition ofthe desired or required solids content. Hence, although the rates atwhich the collagen slurry 10 and the swelling agent 22 are delivered tothe homogenizer are important, they will be dependent upon theconcentrations of the collagen and swelling agent to be mixed which, inturn, will be dependent upon the final collagen composition desired orrequired to be obtained.

In the homogenizer 20, the swelling agent 22 and the collagen slurry 10are blended and the collagen imbibes liquid (swells). The resultant,eXtrudable or formable composition can then be processed as desired toyield a formed product as, for example, leather-like fibrous materialssuch as are use for the production of shoes, filters such as are usedfor cigarettes, tubular casings such as those employed in producingsausages, filaments such as are used for sutures, and the like.

The mixing of the collagen and swelling agent, even under conditions ofextensive processing with recirculation, can fail to provide the degreeof homogeneity required for continuous extrusion of thin casings such asthe type employed for producing sausage products. The structure andmethod of operation of the homogenizer 20, is therefore, of the ulmostcriticality.

One embodiment of an homogenizer 20 which can be utilized in thepractice of the present invention is shown in more detail in FIGS. 2 and3. As shown therein, the homogenizer 20 comprises a cylindrical rotor 30rotatably mounted on shaft 31 which, in turn, is connected to a suitabledrive means such as an electric motor (not shown). Surrounding rotor 30is a cylindrical stator housing 34 4 having a smooth inner surface. Acooling jacket 38 equipped with inlet means 37 and outlet means 39, isprovided about stator 34.

As can be seen more clearly in FIG. 3, rotor 30 is provided with aplurality of projections 32 on its outer circumferential surface. Theconfigurations of the projections 32 on the outer circumferentialsurface of the rotor 30 and the smooth inner circumferential surface ofthe stator 34 are important to the extent that coaction between thesesurfaces must produce a gradual, continuous shredding of any lumpspresent in the collagen slurry and result in uniform homogenization ofthe slurry as it progresses axially from the inlet end at inlet ports26, 28 to the discharge outlet 40 of the homogenizer.

The annular space between the inner surface of the stator 34 and theouter surface defined by the circumferential plane formed by the uppersurfaces of the projections 32 and identified by reference numeral 36,must be small enough to insure a high shear rate of the collagen slurry.It has been found that this distance 36 should be on the order of fromabout 0.005 to 0.015 of an inch and, advantageously, about 0.010 of aninch so that the collagen slurry can be mixed to obtain acorrespondingly thin layer having a thickness of about the samedimensions. Preferably, the collagen slurry is in the form of a thinsheet-like mass as it is subjected to the shearing action in thehomogenizer so that there is provided a maximum surface-to-volume ratioof the sheet-like mass. Under these conditions, proper and effectiveshearing is provided and results in obtaining a uniformly homogenizedcomposition. The efifective heat removal ability of the cooling jacket38 is thusly also enhanced, thereby significantly decreasing orsubstantially eliminating any degradation since the slurry being cooledis spread thin.

It has also been found that the height of the projections 32 should befrom about 0.03 of an inch to 0.09 of an inch to obtain adequateresults. Preferably, the height of the projections should be about 0.03of an inch. The projections can have various configurations such asrectangular, square, oval, hemispherical and the like, as desired orrequired. The projections 32 need not extend the full length of therotor 30 and can vary in size or configuration along the length of therotor. Preferably, however, projections 32 are provided along the entirelength of the rotor 30.

Rotor 30 can be conveniently fabricated to be about 2.5 inches indiameter and about 4.5 inches in length to provide a system capable ofhandling a collagen slurry throughput on the order of about 2.5kilograms/hour and in which the dwell time of the slurry is on the orderof from about 30-40 seconds. Adequate homogenization of the collagenslurry can most readily be achieved while minimizing degradation throughthe expedient of increasing the lengths of the rotor 30 and the stator34.

The embodiments of the apparatus of the present invention can beemployed for a continuous, one-pass mixing of fibrillated collagenslurry with a liquid swelling agent.

With reference first to FIG. 1 of the drawing, a typical operation ofthe apparatus will now be described.

The pressurized vessel 12 is charged with the desired collagen slurry10. An air pressure of from about 30 to pounds per square inch (p.s.i.)can be employed in the pressure vessel 12 to force the collagen slurry10, which can contain up to about 8.0% solids, to metering pump 1.8.Metering pump 18, in turn, delivers a metered quantity of the collagenslurry 10 under pressure through conduit 19 and inlet port 26 of thehomogenizer 20. Similarly, the swelling agent 22, which is preferably adilute aqueous acid, such as 1.54% to 2.24% lactic acid solution, issupplied under pressure through conduit 25 to the homogenizer 20 by pump24.

The ratio of the acid to collagen and the acid pH are adjusted to obtaina collagen-swelling agent blend having a pH of about 4.0. By regulatingthe relative speeds of metering pumps 18 and 24 suflicient pressure andan efficient flow rate control of the blend through the homogenizer canbe provided as desired or required.

The swelling agent solution 22 can be cooled to as low a temperature aspractical prior to its being pumped to the homogenizer 20. The lowtemperature of the swelling agent 22 helps to retain a low temperaturein the resultant collagen-swelling agent blend during the subsequentmixing and shearing operation in the homogenizer 20 and thus helps toavoid collagen degradation. However, it is important that thetemperature of the swelling agent be sufficiently high to avoid itsfreezing or freezing of the collagen slurry, or otherwise interfere withthe ability of the collagen to imbibe liquid.

The collagen slurry 10 and swelling agent 22 enter through inlet ports26 and 28, respectively (FIGS. 2 and 3). A low acid inlet is preferredto facilitate air purging when the homogenizer is initially filled withacid.

In the practice of the present invention, separate, spaced inlets arerequired for the collagen slurry and for the swelling agent. However,additional additives, whose use is known to those skilled in the art,can also be premixed with either the swelling agent or collagen slurryor can be fed separately to the homogenizer through an additional inletor a plurality of inlets. Exemplary of these additives are suchingredients as dyes, pigments, diluents, pore formers, blowing agents,flavoring agents, hardening agents and the like, as Well as shrinkcontrol agents typified by such materials as synthetic fibers such ascellulose, cotton and rayon; or such materials as alginates, starches,and the like.

The use of a plurality of inlets for each ingredient or component as,for example, in a system in which every other inlet of a series ofradially displaced inlets is connected to the collagen slurry supply andthe remaining inlets are connected to the swelling agent supply, has theadvantage of providing a larger degree initial mixing.

A liquid coolant, such as silicone oil, alcohol, glycol and the like,can be circulated through cooling jacket 38 at a temperaturesufficiently low to prevent the discharge temperature from thehomogenizer 20 from rising above 20 C. and, preferably not above 15 C.,but high enough so that the collagen slurry and swelling agent do notfreeze.

The optimum speed of rotation of the rotor 30, will be somewhatdependent upon the throughput, viscosity, rotor design and clearancesbetween the planar surfaces of the rotor 30 and the stator 34 as well asthe operating temperatures. The speed at which the rotor 30 is drivenshould be such as to maintain a product discharge temperature at outlet40 below about 20 C., and preferably below 15 C. in order to avoidcollagen degradation.

\It is preferred that all process steps such as swelling, dispersing,extrusion or forming of the collagen be conducted at temperatures not toexceed about 15 C. in order to minimize degradation.

The collagen supplied to the homogenizer can be prepared in variousmanners. The following examples of collagen preparation and pretreatmentprocedures are illustrative of the various possible procedures which canbe employed and are not intended to indicate the limits of theinvention. Parts and percentages are by weight, unless otherwiseindicated.

EXAMPLE I Nonbifurcated, deep flexor, bovine tendons were manuallycleaned and scraped to remove adhering refuse such as tendon sheath,fat, hair and the like. Twenty-four hundred grams (gms.) of the cleanedtendon was then mixed with 2300 gms. of crushed ice and ground in aconven tional meat grinder. A plate with inch holes was used for thefirst pass through the grinder and a plate with A; inch holes was usedfor the second pass. The temperature as measured with a glassthermometer inserted into the mass was C. The mixture had the appearanceof white, coarsely ground meat.

Twenty-three hundred grams of Water was added to the ground collagen bymanual mixing. The mixture was then passed four times through a meatemulsifier precooled to about 5 C. with ice, characterized in that itwas driven by a 28 horsepower motor, had a superfine plate having holes1.7 millimeters (mm) in diameter and a high speed cutting head. The meatemulsifier was cooled to offset the heat generated by mechanical actionand to maintain the temperature of the collagen mass at no greater than15 C. The emulsified collagen mass had the consistency of uncookedsausage emulsion.

The resultant fibrillated collagen showed, under microscopicexamination, a shrink temperature essentially identical to that oftendom (66-68 C.) which indicated there had been no substantialdegradation. The term shrink temperature refers to the temperature atwhich the collagen fibers, in contact with water, contract to aboutonethird to one-quarter of their initial length.

The resultant fibrillated collagen was then ready for mixing with aswelling agent.

EXAMPLE II The process of Example I was followed, except that beef hide,from which the hair layer and flesh-side impurities had been removed,was substituted for the beef tendon.

MIXING PROCEDURES EXAMPLE III The fibrillated hide of Example II wasdiluted with Water to form a suspension having a 4.72% solids content.This slurry was maintained under a pressure of 60 p.s.i. in apressurized vessel which was cooled to 0 C. with an ice water bath.

The aqueous collagen slurry was then pumped at a rate of 395 cc./min. tothe upper inlet of a homogenizer of the type shown in FIGS. 2 and 3.

A 2.24% lactic acid solution was simultaneously metered by means of aconventional metering pump at a rate of 15.4 cc./min., to the lowerinlet of the homogenizer.

The rotor of the homogenizer measured 4.5 in. in overall length, 2.5 in.in diameter and had a series of 0.062 in. high projections, 0.13 in.square, along the first 3.12 inches of its length. The stator had asmooth inner wall and the clearance between the uppermost planar surfaceof the projections and the inner surface of the stator was measured at0.010 inch.

The rotor speed was maintained at about 290 rpm.

Alcohol at a temperature of 25 C. was circulated through the coolingjacket and served to maintain the collagen dispersion temperature at theoulet at 15 C.

The resultant mass was translucent and did not have the opacityassociated with the usual non-uniformly swollen dispersions.

The swollen collagen blend was then extruded to form a tubular casingand the casing was stuffed with standard pork sausage emulsion and friedin a covered electric fry pan at 300 F. Three tablespoons of water wereadded to the cold pan and sausages placed therein. After five minutes,the cover was removed and the sausages turned until brown. Duringfrying, the casings did not split, nor was meat exposed or extruded fromthe ends of the encased sausages. The casing conformed to the meat andresulted in a pleasing, attractive product. The casing did not impart aflavor to the sausage and was comestible with the meat.

EXAMPLE IV To provide a control, the following operation was carried outin a homogenizer which was not equipped with a rotor or have arotor-stator clearance in accordance with the apparatus of the presentinvention. The homogenizer was of the type generally shown in FIGS. 2and 3 to the extent that it included; a swelling agent inlet, a collagenslurry inlet, a paddle type rotor, a stator, and an 7 outlet for themixed product. The rotor was of the type disclosed in US. Pat.3,150,862, FIG. 4.

Ground, pretreated fibrillated collagen in the form of an aqueous slurryhaving a 6% solids content was maintained under a pressure of 60 p.s.i.in a pressurized vessel. The vessel was cooled by a C. ice water bath.

The aqueous collagen slurry was pumped at a rate of about 77 to 88cc./min. to the upper inlet of the homogenizer and a 0.5%perfluorobutyric acid solution was simultaneously metered at a rate of14.8 to 19.0 cc./min., to the lower inlet of the homogenizer.

The resultant, viscous, swollen, collagen mixture contained portions ofcollagen that were highly swollen and portions that were substantiallyunswollen. Clumps of unswollen collagen fibers were matter together andencapsulated by a coating of viscous swollen collagen.

Further variations of the foregoing operation did not yield a mixturewhich could be considered to be a uniform composition. For example, aprolonged, slow mixing of the homogenizer failed to adequatelyredistribute the swelling agent or reduce the size or number of thereadily deformable clumps while rapid mixing caused localizedoverheating and excessive degradation of the collagen.

EXAMPLE V Pretreated, fibrillated collagen obtained by the proceduredescribed in Example 11 above was diluted with water to a 7.8% solidscontent and acidified slightly to a 0.05% acid content with a lacticacid solution. The collagen slurry was then metered to the homogenizerof the present invention at a rate of 89 cc./min. and mixed therein witha dilute lactic acid solution metered to the homogenizer at a rate of15.6 cc./min.

The rotor of the homogenizer was run at a speed of 180 r.p.m., and thealcohol coolant in the cooling jacket was maintained at a temperature ofbetween about 15 C. and -20 C.

The resultant, swollen collagen dispersion was discharged from thehomogenizer, at a temperature of 14 C. and had a 6.97% solids content.

Hand made tubular film fabricated from the swollen collagen exhibited atensile strength of 79.3 lb./g. mass/ in. of flat width. The tubularfilm was then stuffed with pork sausage and remained intact duringsubsequent frying of the encased pork sausage.

Although the invention has been described with particularity and in somedetail, it should be understood that various changes, modifications andalterations can be made therein without departing from the spirit andscope of the invention.

What is claimed is:

1. A process for producing a formable collagen dispersion including thesteps of:

(a) forming an air-free collagen slurry;

(b) simultaneously metering through separate conduits the collagenslurry and an air-free collagen swelling agent to an homogenizing mixingzone;

(c) mixing together the metered proportions of collagen slurry and thecollagen swelling agent in the homogenizing mixing zone the mixture inthe form of a sheet-like mass being immediately subjected to shearingaction;

(d) continuing to subject the thin sheet-like mass of collagenslurry-swelling agent mixture to the shearing action until a uniformdispersion is obtained and the collagen is uniformly swollen; and

(e) discharging the uniformly swollen collagen from the mixing zone.

2. The process of claim 1 wherein the collagen slurry delivered to themixing zone has a solids content of from about 3-15% by weight.

3. The process of claim 1 wherein the collagen slurry delivered to themixing zone has a solids content of from about 6% to 8% by weight.

4. The proces of claim 1 wherein the temperature of the mixing zoneduring the mixing of the collagen slurry and the swelling agent does notexceed about 20 C.

5. The process of claim 1 wherein the collagen slurryswelling agentmixture is maintained at a thickness of from about 0.005 to 0.015 of aninch during shearing.

6. A process for producing a formable collagen dispersion including thesteps of:

(a) forming an air-free aqueous collagen slurry having a solids contentof from about 3%15% by weight;

(b) metering through a separate conduit the collagen slurry to anhomogenizing mixing zone where the collagen slurry in the form of asheet-like mass is subjected to shearing action;

(0) simultaneously metering through a separate conduit an air-freecollagen swelling agent to the homogenizing mixing zone and mixingtogether the sheet-like mass of collagen and the collagen swelling agentas the sheet-like mass of collagen is subjected to shearing action;

((1) continuing to subject the collagen slurry-swelling agent mixture tothe shearing action until a uniform dispersion in the form of asheet-like mass having a thickness of from about 0.005 to 0.015 inch isobtained;

(e) maintaining the mixing zone during the shearing at a temperature offrom about 15 C. to 20 O;

(f) continuing the shearing of the collagen slurryswelling agent mixtureuntil the collagen is uniformly swollen; and

(g) discharging the uniformly swollen collagen from the mixing zone.

7. The process of claim 6 wherein the collagen slurry delivered to themixing zone has a solids content of from about 6%--8% by weight.

8. The process of claim 6 wherein the collagen slurryswelling agentmixture has a thickness of about 0.010 of an inch.

References Cited UNITED STATES PATENTS 2,115,484 4/1938 Dewsbury et al.252-311 2,120,851 6/1938 Becker et al. 106-155 X 2,919,998 1/1960Klevens et al. 260-123] X 3,303,038 2/1967 Klevens 106155 3,433,8643/1969 Highberger et al. 260-123] X RICHARD D. LOVERING, PrimaryExaminer US. Cl. X.R.

